Published January 20, 2015
LACTATION BIOLOGY SYMPOSIUM: Circadian clocks
and photoperiod in mammary gland development and lactation1
D. L. Hadsell2
Department of Pediatrics, The USDA/ARS Children’s Nutrition Research Center,
Baylor College of Medicine, Houston, TX 77030
©2012 American Society of Animal Science. All rights reserved.
J. Anim. Sci. 2012. 90:742–743
http://dx.doi.org/10.2527/jas.2011-4983
Life on earth evolved with light-dark cycles. As a result there arose in all organisms, though probably first
in photosynthetic archaebacteria, oscillatory mechanisms to time processes that were necessary for survival and reproduction (Woelfle et al., 2004). The first
known account of these oscillations was given for plants
in the 4th century BC by Androsthenes, a ship captain under Alexander the Great (reviewed by McClung,
2006). It was not until the early 20th century, however,
that the presence of ~24-h patterns of activity in the
absence of external queues was observed in mammals.
In 1959, Franz Halberg coined the term circadian from
the Latin words “circa” (about), and “dies” (day) to
describe these ~24-h oscillations that are now known
to occur in all living organisms.
The Lactation Biology Symposium on “Circadian
Clocks and Photoperiod in Mammary Gland Development and Lactation” was held at the Joint Annual
Meeting of the American Society of Animal Science
and the American Dairy Science Association in New
Orleans, Louisiana, July 11 to 15, 2011. The objective
of the symposium was to provide the lactation biology
community with new insights and perspectives from recent research findings on circadian biology as it related
to mammary gland development and lactation.
The molecular mechanism governing circadian oscillations first became apparent in the early 1980s and
1990s with the cloning of the clock genes, first in Drosophila and then in mammals. In lactating mammals,
diurnal rhythms have been described for several behavioral and physiological traits. Hardin (2011), as the first
speaker of the symposium, gave a historical perspective
of circadian biology and provided an introduction to
the concepts of endogenous circadian clocks and en-
trainment. He then went on to present events leading to
the discovery and description of molecular clock mechanisms in the fruit fly, Drosophila melanogaster, and
compared these with the molecular clock mechanisms
described in higher organisms and mammals.
As the second speaker of the symposium, Porter
(2011) described the developmental changes that occur
in the expression of Period (per)1, per2, and brain and
muscle aryl hydrocarbon receptor nuclear translocatorlike 1 genes within the murine mammary gland. He presented data to indicate that per genes interact with cell
cycle DNA damage checkpoint proteins and are downregulated in mammary cancer. Using the technique of
mammary tissue grafting, he demonstrated that per1
and per2 are necessary for normal mammary ductal development and the maintenance of mammary epithelial
cell polarity.
Casey and Plaut (2012), the third presentation for
the symposium, reviewed the concept of homeorhetic
adaptation, gave an overview of circadian and photoperiod biology in mammals, and reviewed recent data
demonstrating the mRNA transcripts for core clock
components in the mammary tissue of lactating rats as
well as in RNA derived from human breast milk. Data
were also presented to support the hypothesis that peripheral circadian clocks play an important role in the
regulation of homeorhetic responses to the onset of lactation in dairy cows. In a microarray study comparing
changes in gene expression with secretory activation
among mammary tissue, liver, and adipose tissue, an
induction of the positive limb of the core clock was
observed in all 3 tissues, and the negative limb of the
core clock was also suppressed. In addition, analysis of
bovine milk-fat globule RNA demonstrated circadian
oscillations in the transcripts of core clock components
that were correlated with changes in milk composition.
The symposium concluded with a review on impacts of photoperiod on mammary gland development
and lactation in the cow (Dahl et al., 2012). Long-day
photoperiod is known to increase milk production in
dairy cows when applied during lactation. In addition,
long-day photoperiod also enhances overall growth and
mammary gland development in calves and heifers, ul-
1
Based on a presentation at the Lactation Biology Symposium titled “Circadian Clocks and Photoperiod in Mammary Development
and Lactation” at the Joint Annual Meeting, July 10 to 14, 2011,
New Orleans, Louisiana, with publication sponsored by the Journal
of Animal Science and the American Society of Animal Science.
2
Corresponding author: [email protected]
Received December 2, 2011.
Accepted December 3, 2011.
742
2011 Lactation Biology Symposium
timately leading to animals capable of producing more
milk. On the other hand, short-day photoperiod during
the dry period is beneficial to the subsequent lactation.
Although the mechanism through which this occurs is
complex, there are indications that a phylogenetically
conserved interaction between melatonin and prolactin
is involved, that IGF-I has a role, and that the effects
are mediated through changes in mammary gland development.
In summary, the development of the mammary gland
and lactation are subject to regulation by a set central
and peripheral clock molecules that appear to be conserved across species. The work presented provides a
useful basis for further studies aimed at understanding
how peripheral clocks regulate the various aspects of
mammary gland development and what their potential
role is in determining milk production. It is only a matter of time.
743
LITERATURE CITED
Casey, T. M., and K. Plaut. 2012. LACTATION BIOLOGY SYMPOSIUM: Circadian clocks as mediators of the homeorhetic
response to lactation. J. Anim. Sci. 90:744–754. doi:10.2527/
jas.2011-4590.
Dahl, G. E., S. Tao, and I. M. Thompson. 2012. LACTATION BIOLOGY SYMPOSIUM: Effects of photoperiod on mammary
gland development and lactation. J. Anim. Sci. 90:755–760.
doi:10.2527/jas.2011-4630.
Hardin, P. 2011. Circadian timekeeping mechanisms. J. Anim. Sci.
89(E-Suppl. 1):185. (Abstr.)
McClung, C. R. 2006. Plant circadian rhythms. Plant Cell 18:792–
803.
Porter, W. 2011. Circadian clocks in mammary gland development
and differentiation. J. Anim. Sci. 89(E-Suppl. 1):185. (Abstr.)
Woelfle, M. A., Y. Ouyang, K. Phanvijhitsiri, and C. H. Johnson.
2004. The adaptive value of circadian clocks: An experimental
assessment in cyanobacteria. Curr. Biol. 14:1481–1486.